Title page for ETD etd-11122009-130445

Investigation of the Energy Variation on a TomoTherapy HI-ART II Using an Aluminum Stepwedge

Degree

Master of Science (M.S.)

Department

Physics & Astronomy

Advisory Committee

Advisor Name

Title

Gibbons, John

Committee Chair

Fontenot, Jonas

Committee Member

Hogstrom, Kenneth

Committee Member

Matthews, Jim

Committee Member

Keywords

tomotherapy

determination of energy

Date of Defense

2009-10-20

Availability

unrestricted

Abstract

Purpose: To determine the sensitivity of a topographic stepwedge procedure to energy variations in a helical tomotherapy system.

Method and Materials: Topographic procedures were followed using an aluminum stepwedge suspended in air on the end of the couch for a TomoTherapy HI-Art II system. Exit detector data from these procedures, collected and processed using TomoTherapy quality assurance (TQA) software were used to determine the effective beam energy. Energy sensitivity tests of the technique were made by varying the injector current. Topographic procedures were run daily over the lifetime of an x-ray target. Additionally, water phantom scanning data (lateral profiles and percent depth dose) were measured monthly over the same time period.

Results: The attenuation data from the stepwedge demonstrated a smooth decrease in effective energy with time over the life of the target. The energy difference showed dramatic spikes in trending due to target changes and injector current adjustments. Monthly lateral and depth-dose profiles showed variations due to an energy change but not while a target was simultaneously degrading. Analysis of the data show that the stepwedge procedure is capable of detecting a change in the effective energy of greater than 2%.

Conclusion: The stepwedge topographic procedure provides a good method to monitor the energy difference over time and may be used to help diagnose impending target failures.